The organic extract of the leaves and stems of two plants, Excoecaria guineensis and Combretum bracteatum, were active in the NCI anti-HIV assay. The extracts were also found to give positive results in a phorbol ester binding assay. Tandem application of these two assays to direct separations led to the identification of the dihydroxy carotenoid lutein as the major active compound in Combretum; lutein was also isolated from Excoecaria extracts. The behavior of lutein and several related xanthophylls in a battery of secondary screens is being investigated.